ES2914412T3 - Out-of-plane jointing for micro and nanoelectromechanical systems with reduced nonlinearity - Google Patents

Abstract

Articulation between at least one first element (S) and at least one second element (M) of a microelectromechanical system, said first element (S) and said second element (M) being movable relative to each other at least in one direction away from flat, said joint comprising a first rigid part (4), a second part (6) integral with the first part (4) at one end and intended to be anchored in the first element, said second part (6) being configured to be deformable in bending in a first direction (Z), and two third parts (8) integral with the first part (4) and intended to be anchored in the second element, the third parts (8) being configured to be deformed in bending along a second direction (X) orthogonal to the first direction (Z).

Description

DESCRIPTION

Out-of-plane jointing for micro- and nanoelectromechanical systems with reduced nonlinearity

Technical field and prior art

The present invention relates to an out-of-plane joint for microelectromechanical and/or nanoelectromechanical systems that offer reduced nonlinearity and to a system that implements at least two such joints.

Microelectromechanical systems or MEMS (microelectromechanical systems in Anglo-Saxon terminology) and micro and nanoelectromechanical systems or M&NEMS systems (micro & nanoelectromechanical systems in Anglo-Saxon terminology) are used to make sensors or actuators. They comprise at least one mobile element with respect to a substrate. For example, in the case of a sensor, the displacement of the moving part or mass is measured and can be translated into a characteristic to be detected, for example, an acceleration, and in the case of an actuator, the moving element is moved, for example, by means of electrostatic forces, for example, to displace a micromirror.

The moving element is suspended with respect to the substrate and depending on the applications it may be desired to have a displacement in the plane of the system or a displacement out of plane, that is, orthogonal to the plane of the system.

When the movable member has a large amplitude displacement in the out-of-plane direction, the connecting region may exhibit significant non-linearity.

This nonlinear behavior is illustrated in Figures 1A to 1C. The mobile mass M is suspended to the substrate S by a joint A formed by a thin membrane. The displacement in the Z direction of the mass M causes a deformation of the membrane in the first order in the Z direction and in the second order in the X direction. When the displacement of the mass in the Z direction is significant, the elongation of the membrane in the X direction (Figure 1B) is no longer insignificant. As a result, the retractive force exerted by the membrane on the mass is nonlinear (Figure 1C) and varies significantly with displacement in the Z direction. This nonlinearity can substantially affect the response of the system, for example, in the case of a sensor, and can make the sensor unreliable.

Prior art document US 2015/033860 A1 describes an articulation between at least one first element and at least one second element of a microelectromechanical system, said first element and said second element being movable relative to each other at least in one direction away from each other. flat, said articulation comprising a second part intended to be anchored in the first element, said second part being configured to deform in bending in a first direction, and two third parts intended to be anchored in the second element, the third being portions configured to deform in bending along a second direction orthogonal to the first direction.

Exhibition of the invention

Therefore, it is an object of the present invention to provide an articulation for a MEMS or M&NEMS system capable of exhibiting low non-linearity and a MEMS or M&NEMS system whose moving part may have significant out-of-plane translational displacement while exhibiting low non-linearity. low nonlinearity.

The objective stated above is achieved through an articulation intended to connect a first element and a second element of a MEMS or M&NEMS system, comprising a first part rigid in the three directions of space, a second part connected to the first part and intended to be connected to the first element, the second part being thin and intended to extend in the plane of the system, and capable of being flexurally deformed in the out-of-plane direction, and two third parts configured to be flexurally deformed in the plane , the two third parts being each connected to one end of the first part such that, when there is a relative displacement between the first and second elements in the first direction, the first part deforms in bending in the out-of-plane direction and two-thirds are deformed in bending along a plane direction. The third parts then offer an elongation in the plane that makes it possible to limit the deformation of the first part in the plane, and therefore reduces the non-linearity of the joint.

Thanks to the invention, the deformation in the plane of the first part is reduced, even avoided by the slight bending of the third parts that accompany the first part in its displacement in the plane.

In other words, a composite joint is made that comprises several parts that each ensure a good function and that make it possible to reduce the non-linearity of the joint. The joint combines at the same time a joint obtained by an element stressed in bending in the out-of-plane direction and a joint obtained by the elements configured to deform in bending according to a direction in the plane, which makes it possible to offer the possibility of a displacement of large amplitude in the out-of-plane direction while retaining a low degree of nonlinearity.

Very advantageously, each part can be designed to adapt the properties of the joint based on the needs, for example, the flexibility in the out-of-plane direction can be varied and/or the guidance in a certain direction can be improved.

Advantageously, a MEMS or M&NEMS system includes at least two joints which ensures very good guidance in the out-of-plane direction and at least one guidance in an in-plane direction.

Very advantageously, the MEMS or M&NEMS system includes at least three articulations, and even more advantageously four articulations, making it possible to ensure guidance in the out-of-plane direction and very good maintenance in both directions of the plane.

Therefore, the object of the present invention is an articulation between at least one first element and at least one second element of a microelectromechanical system, said first element and said second element being movable relative to each other at least in an out-of-plane direction. , the said articulation comprising a first rigid part, a second part integral with the first at one end and intended to be anchored to the first element, said second part being configured to be deformable in bending in a first direction, and two third parts integral of the first and intended to be anchored in the second element, the third parts being configured to deform in bending along a second direction orthogonal to the first direction.

In an advantageous example, in an undeformed state, the third parts extend in a plane orthogonal to a plane in which the second part extends.

Preferably, the second part has a dimension in the first direction reduced with respect to the dimensions in the other directions.

For example, the first part extends, in the first direction, between a first plane and a second plane, and the second part includes a face located in one of the first and second planes.

Preferably, the third parts comprise at least two blades, which extend over at least part of the dimension of the first part in the first direction, for example over the entire dimension of the first part in the first direction.

In an exemplary embodiment, each third part includes a blade, the two blades being coplanar and being arranged so that they also deform in torsion. Therefore, the joint is more flexible in the out-of-plane direction.

In another exemplary embodiment, each third part includes two blades, one blade of each third part being coplanar with a blade of the other third part, and the two blades of a third part are arranged with respect to each other so that they do not deform or deform little in torsion. The blades allow the linearity of the joint to be obtained without modifying little or nothing the out-of-plane stiffness of the joint.

The second parts may advantageously include a lattice structure so as to ensure flexibility in the first direction and a certain stiffness in at least a third direction orthogonal to the first and second directions.

For example, the second part has a thickness in the first direction between a few hundred nm and a few micrometers, a length in the third direction and a width in the second direction between a few pm and a few hundred pm.

For example, the thirds have a thickness in the first direction between 10 pm and a few tens of pm, a width in the second direction of the plane between 100 nm and a few micrometers, and a length in the third direction between a few pm and a few tens of pm.

For example, the first part has a thickness in the first direction, a length in the third direction and a width in the second direction between a few pm and a few hundred pm.

The present invention also has as its object a microelectromechanical system comprising a first element and at least one second element, movable with respect to each other at least in one out-of-plane direction, and at least two joints according to the invention, each one anchored to the first element and to the second member, and the hinges are oriented so that the first direction is the out-of-plane direction and the second and third directions are the in-plane directions.

The at least two joints are arranged symmetrically with respect to a plane of symmetry of the moving part, said median plane containing the out-of-plane direction.

For example, the second plane is on the fixed part side and the second part includes a face that extends into the second plane.

The system may include at least four joints such that the axes of the twists of the third parts of the joints are arranged orthogonal to each other.

According to an additional feature, the microelectromechanical system includes the means for setting the second element in motion at least in one out-of-plane direction.

The microelectromechanical system is, for example, a microphone.

Brief description of the drawings

The present invention will be better understood on the basis of the following description and the accompanying drawings in which:

Figures 1A and 1B are side views of a prior art MEMS system at rest and in a state where the mass has moved in the out-of-plane direction and illustrating the elongation of the joint;

- Figure 1C is a graphical representation of the elongation of the joint of Figures 1A and 1B, in the X direction based on the displacement of the mass in the Z direction;

- Figure 2 is a perspective view of an example of a joint according to the invention;

- Figure 3 is a detailed view of Figure 2;

- Figure 4 is a top view of the joint of Figure 2;

- Figure 5 is a perspective view of an example of the M&NEMS system comprising joints according to the invention,

- Figure 6 is a top view of another example of the M&NEMS system comprising joints according to the invention,

Figure 7 is a top view of another example of the system comprising the joints according to the invention in a state of rest and in a state of movement out of plane;

- Figure 8 is a view from above of another example of the system comprising three joints according to the invention, - Figure 9 is a view from above of another example of the system comprising four joints according to the invention, - Figure 10 is a top view of another embodiment of a joint in which the third parts deform substantially only in bending.

Detailed exposition of the particular embodiments

In the present application, a "microelectromechanical system" or "MEMS system" refers to a micro and/or nanoelectromechanical system, that is, one that comprises elements that have micrometric dimensions and/or elements that have nanometric dimensions.

In Figures 2, 3 and 4 an example of a joint 2 according to the invention can be seen. In dashed lines, a fixed part or substrate S of a microelectromechanical system and a moving part or mass M intended to be suspended from the substrate S by the articulation 2 are represented. It will be understood that the articulation can make the articulation between two moving parts with each other, and themselves mobile with respect to a fixed substrate.

The articulation 2 is intended to allow an out-of-plane displacement of the mobile part M.

The plane of the system is defined by the X and Y directions, and corresponds to the median plane of the system in which the moving mass M extends, it is also the median plane of the fixed part.

The out-of-plane Z direction is orthogonal to the system plane.

The joint includes a first rigid part 4.

"Rigid part or element" is understood as an element that does not deform or little under the effect of the stresses generally applied to a MEMS system in the case of a sensor or an actuator in normal operation.

In the example shown, the first part 4 has the shape of a parallelepiped beam having a thickness Tb, a width Wb and a length Lb. The first part extends in the Z direction between a parallel first plane P1 and a second parallel plane P2.

The thickness Tb corresponds to the dimension of the beam in the Z direction, the width Wb corresponds to the dimension of the beam in the X direction, and the length Lb corresponds to the dimension of the beam in the Y direction.

The dimensions Tb, Wb and Lb are, for example, between a few pm and a few hundred pm.

The joint 2 includes a second part 6 that has a low thickness Tm with respect to its length Lm and its width Wm so as to allow its bending deformation along the Z direction. The ratios Tm/Wm and Tm/Lm are, for example , between 1/100 and 1/10.

For example, its thickness Tm is between a hundred nm and a few hundred nm, its length Lm and its width Wm are between a few pm and a few hundred pm.

Therefore, the second part 6 is in the form of a membrane that is integral with the first part 4 by a first edge 6.1 extending in the direction Y, and by a second edge 6.2 parallel to the first edge 6.1 and intended to be in solidarity with the mass M.

The membrane is arranged in the example shown in the plane P2 that delimits the lower face of the first part in the example shown. Furthermore, in the example shown, the lower face of the mass M is also contained in the plane P2.

As a variant, the membrane could be anchored to the mobile part in any position between the planes P1 and P2.

The articulation 2 includes two third parts 8 that form the blades and are secured by an edge 8.1 to one end of the beam 4.1, 4.2 along the Y direction. Furthermore, the blades extend in the YZ plane.

The blades are dimensioned to be able to deform in bending in the X direction. For example, the blades have a thickness TI between 10 pm and a few tens of pm, a width Wl between 100 nm and a few micrometers, and a length LI between a few pm and a few tens of pm.

In the example shown, the blades 8 extend in a mean plane R of the beam parallel to the plane YZ.

The blades 8 are intended to be anchored in the fixed part S by an edge 8.2 parallel to the edge 8.1.

In Figure 5, a MEMS system 10 can be seen that implements two joints 2. The joints 2 are anchored in the mobile part M symmetrically with respect to a plane of symmetry of the mobile part M parallel to the YZ plane.

The membranes 6 are anchored on the parallel faces M.1, M.2 of the mobile part M.

The blades are anchored in the fixed part S.

In the representation of Figure 5, the movable part M has an out-of-plane movement upwards, the membranes are deformed in bending and the blades 8 are deformed in bending in the X direction. The two blades 8 will also be deformed in torsion around of the Y axis, which allows to reduce the stiffness of the joint.

The operation of the joint will now be described using Figure 5.

Considering the application to a sensor, for example an accelerometer intended to measure acceleration in the Z direction.

When the mobile part moves out of plane under the effect of an acceleration along Z, the two membranes 6 are deformed in bending accompanying the movement of the moving part along Z, the blades 8 are deformed in bending along the direction X and also in torsion around the Y axis.

The bending deformations of the blades 8 according to X allow the beams 4 to move in the X direction, and the edges of the beams 4, to which the edges 6.1 of the membranes are fixed, accompany the membranes 6 in their deformation according to the X-direction. This results in a reduction in the variation of the structure's stiffness, and therefore a reduction in the degree of non-linearity. The membranes are mainly deformed in the Z direction and are no longer stretched along X. Thanks to the invention, the joints retain a low degree of non-linearity even for large amplitude Z displacements.

The moving part is guided according to the Z direction.

The joints 2 present a great rigidity according to the Y direction, therefore, the mobile part is very well maintained in the Y direction. In addition, the joints 2 also ensure a maintenance of the mobile part M in the X direction. To improve the hold in the X direction, it is advantageous to add at least a third joint 2, the three joints 2 being distributed at 120° to each other around the mobile mass M' as schematically represented in Figure 8.

In Figure 9, the system includes four joints 2 arranged at 90° to each other. Each articulation 2 is anchored to an edge of the mobile mass M''.

The system configurations of Figures 8 and 9 ensure very good maintenance of the moving parts M in the XY plane and their guidance in the Z direction.

In Figure 10, another example of embodiment of a joint can be seen, in which the blades 8' deform almost only in bending in the X direction.

In this example the joint includes a pair of blades 8' at each end of the beam 4.

The blades 8' of each pair are positioned parallel to each other in the YZ plane. In this example, one of its faces is aligned with a beam face parallel to the YZ plane. The implementation of two parallel blades 8' at each end makes it possible to block the torsional deformation of each of the blades. The two blades 8' of each pair individually have a tendency to torsionally deform, but in combination each blade 8' prevents the other blade 8' from torsionally deforming during out-of-plane movement of the movable part M. Therefore, the blades deform mainly in bending and accompany the displacement of the membrane 6 in the plane. The non-linear stiffness of the joint is substantially reduced.

Preferably, the membranes are structured to have shapes that ensure high flexibility according to Z and high rigidity in the plane, for example, they include crossbars or trusses and/or they are perforated.

Therefore, it can be seen that the stiffness of the joint in the different directions is determined both by the dimensions of the membrane and by the dimensions of the blades, therefore it is possible to precisely adjust these stiffnesses by acting on the dimensions of the membrane. and/or in the dimensions of the blades. By increasing the thickness of the membrane and/or the width of the blades, the rigidity of the joints is increased, and the displacement of the mass in the Z direction can also be controlled.

The joint has the advantage of offering a very good guide according to Z while being relatively compact due to its low thickness.

It will be understood that the joints may be configured to allow a desired displacement along the X direction. In this case, the blades may be lengthened in the direction of the beam and/or made thinner, offering a certain flexibility in the X direction.

In Figure 6, another example of the MEMS system can be seen that comprises two joints arranged symmetrically with respect to the mobile part M and in which the blades 8 are anchored in the mobile part M and the membranes are anchored in the mobile part. Be fixed.

The operation is similar to that of the system in Figure 5. A very good hold in the Y direction is obtained, and guidance in the Z direction with a low degree of non-linearity.

In Figure 7, another example of the MEMS system comprising four joints can be seen. Two joints 102 are anchored to a first edge M.1 of the mobile mass M and two joints 102 are anchored to a second edge M.2 of the mobile mass M parallel to the first edge.

In this example, the length Lb of the first part 104 is short compared to the length Lm of the blades 108. Furthermore, the membranes 104 have a large width Lm relative to their length Lm.

By way of example, the joints of the system in Figure 7 can have the following dimensions:

Tm=1 |jm; Lm = 10 jm ; Wm = 35 jm

Tb = 20 jm; Lb = 10 jm ; Wb = 4 jm

IT = 18 jm ; LI = 84 jm ; Wl = 1 jm

A set of four joints has a stiffness of 80 N/m

In Figure 7, the mobile part M can be seen in the state of rest, and in an out-of-plane position during displacement. In the example shown, the displacement in the Z direction is of the order of 40 nm. Such a structure allows a displacement of between about 100 nm and about 1 μm.

It will be understood that more than two joints can be implemented side by side.

Furthermore, different numbers of joints anchored to the edges of the mobile part can be implemented.

For example, provision can be made in the system of Figure 7 to implement a hinge on the edge M.3 of the moving part and a hinge on the edge M.4 of the moving part.

The joints of Figures 5 and 6 can be combined, for example, the structure includes a mobile part suspended by two joints according to the invention, one is joined to the moving part by its second part (Figure 5) and the other is joined to its moving part by its third parties.

The articulation according to the invention can be implemented in MEMS sensors for which means are provided for detecting the movement of the mass along Z, for example, capacitive means or piezoresistive or piezoelectric voltage gauges.

The articulation according to the invention can be implemented in MEMS actuators, for which means 12 are provided for actuating the moving part in the Z direction, for example, electrostatic means schematically represented in Figure 7. The electrostatic means comprise at least one pair of electrodes, one being formed on the substrate under the moving part M and the other electrode being formed on the moving part M next to the electrode on the substrate S. The application of a potential difference generates electrostatic forces between the two electrodes and, hence, an out-of-plane displacement of the mobile mass M with respect to the substrate S.

Very advantageously, a MEMS system comprising the articulations according to the invention can be used to make a microphone. In Figure 7, the mobile part M can form a piston that can move in Z under the effect of a pressure differential between its two faces, due to a sound wave.

The joint and the MEMS system can advantageously be fabricated by the known methods of microelectronics by layering and etching. For example, the examples of the manufacturing process described in FR2941533 can be implemented to realize such a MEMS system.

For example, the membranes are formed by the top layer of a silicon on insulator or SOI (Silicon on Insulator in Anglo-Saxon terminology) substrate and the first part and the blades are made by etching and release. As a variant, the membranes are made by deposition of a layer with a thickness of a few hundred nm and the first part and the blades are made by etching and release.

Very advantageously, at least the first part and the third parts are made of the same layer in which the mobile part and part of the fixed part are made.

The system is made, for example, of semiconductor material, such as silicon or SiGe.

Claims (15)

1. Articulation between at least one first element (S) and at least one second element (M) of a microelectromechanical system, said first element (S) and said second element (M) being mobile relative to each other in at least one direction out of plane, said joint comprising a first rigid part (4), a second part (6) integral with the first part (4) at one end and intended to be anchored in the first element, said second part (6) being ) configured to be deformable in bending in a first direction (Z), and two third parts (8) integral with the first part (4) and intended to be anchored in the second element, the third parts (8) being configured to deform in bending along a second direction (X) orthogonal to the first direction (Z). Joint according to claim 1, in which, in an undeformed state, the third parts (8) extend in a plane orthogonal to a plane in which the second part (6) extends. Articulation according to claim 1 or 2, in which the second part (6) has a dimension in the first direction (Z) reduced with respect to the dimensions in the other directions. Articulation according to claim 1, 2 or 3, in which the first part (4) extends, in the first direction (Z), between a first plane (P1) and a second plane (P2) and in which the second part (6) includes a face located in the first plane (P1) or in the second plane (P2). Joint according to one of claims 1 to 4, in which the third parts (8) comprise at least two blades that extend at least part of the dimension of the first part (4) in the first direction (Z ). Joint according to claim 5, in which each third part includes a blade, the blade of a third part and the blade of the other third part being coplanar and being arranged so that they also deform in torsion, or in which each third part includes two blades, one blade of each third part being coplanar with one blade of the other third part and in which the two blades of a third part are arranged with respect to each other so as not to deform or little torsionally deform . Articulation according to one of claims 1 to 6, in which the second parts (6) comprise a lattice structure so as to ensure flexibility in the first direction (Z) and a certain rigidity in at least one third direction (Z). Y) orthogonal to the first (Z) and second (X) directions. Joint according to one of the preceding claims, in which the second part (6) has a thickness (Tm) in the first direction (Z) comprised between a hundred nm and a few micrometers, a length (Lm) in the third direction (Y) and a width (Wm) in the second direction (X) between a few pm and a few hundred pm. Joint according to one of the preceding claims, in which the third parts (8) have a thickness (TI) in the first direction (Z) between 10 pm and a few tens of pm, a width (WI) in the second direction (X) of the plane between 100 nm and a few micrometers and a length (LI) in the third direction (Y) between a few pm and a few tens of pm. Joint according to one of the preceding claims, in which the first part has a thickness (Tb) in the first direction (Z), a length (Lb) in the third direction (Y) and a width (Wb) in the second direction (X) between a few pm and a few hundred pm. 11. Microelectromechanical system comprising at least one first element (S) and at least one second element (M) movable with respect to each other at least in an out-of-plane direction, and at least two joints according to one of claims 1 to 10, each one anchored to the first element (S) and the second element (M), and in which the hinges are oriented so that the first direction is the out-of-plane direction and the second and third directions are the in-plane directions, with the at least two joints advantageously arranged symmetrically with respect to a plane of symmetry of the moving part (M), said median plane containing the out-of-plane direction. 12. Microelectromechanical system according to claim 11 in combination with claim 4, in which the second plane (P2) is on the side of the fixed part (S) and the second part (6) includes a face that extends in the second plane (P2). 13. Microelectromechanical system according to claim 11 or 12, comprising at least four joints such that the axes of the twists of the third parts of the joints are arranged orthogonal to each other. Microelectromechanical system according to one of claims 11 to 13, comprising means (12) for moving the second element (M) in at least one out-of-plane direction. 15. Microelectromechanical system according to one of claims 11 to 14, forming a microphone.